Bone densitometry is divided into two methods: 1, ultrasound means of examination: through the principle of ultrasound to reflect the situation of calcium deposition, can be a good check of bone density and the change of bone structure. Due to the principle of ultrasound, there is no radiation to the body and there is no harm. 2, X-ray examination method: called dual-energy X-ray bone densitometry, mainly through the X-ray penetration of bone, can determine the situation of osteoporosis, there is a certain amount of radiation to the body, but the amount of radiation for one examination is very small. Only try not to choose this kind of examination relative to children, because the radiation is more damaging to children, should try to choose the ultrasound examination method to reduce the harm.